There is a color difference between the added mana cost for Descent of the Void and its follow-up Dark Regression. The normal is to have red text for added mana which is the case for Descent of the Void, but the text for the added mana cost for Dark Regression is beige.
This could only be in the Build Planner and you have taken car of this in the game when it releases but wanted to let you know in case.
https://imgur.com/CaVhFSk